Comparative Evaluation of DC-Link Capacitors for Electric Vehicle Application

In electric vehicle (EV) drive systems, sizing and selection of DC link capacitors involve tradeoffs among system performance including lifetime, reliability, cost, and power density. This paper contributes a comprehensive and comparative study on the DC-link capacitor applications and evaluations to meet the above requirements. The research starts with dynamic modeling of the capacitor equivalent series resistance (ESR) and related ripple current as a function of capacitor type, modulation strategy and load power factor. The analysis considers the facts of capacitor power loss, core temperature, lifetime, and the battery ripple current limit, which are critical for EV applications. The proposed design scheme using film in places of electrolytic capacitors significantly reduces the capacitor size and improves drive system power density from 2.99kW/L to 13.3kW/L without sacrificing system performance. The applications and performance of electrolytic capacitors and film capacitors are experimentally compared and evaluated on a practical 80kW permanent-magnet motor drive system.